1. Field of the Invention
This invention relates to the cooling of combustor dome plates for use in gas turbine engines and more particularly to aircraft gas turbine engine combustors using film cooling for the dome plates.
2. Description of Related Art
Combustor domes generally define the beginning of the combustion section of a gas turbine engine which is located between the compressor and turbine sections of the engine. Combustor domes are used to support the fuel injectors and various air inlet devices to promote complete, efficient, and low pollution emitting combustion particularly in aircraft engine combustors. One such device is an air swirler that surrounds the apertures in the dome plate through which the fuel injectors are disposed in the combustor. Combustor sections generally further include an exterior casing and an interior combustor where fuel is burned producing a hot gas usually at an intensely high temperature such as 3,000.degree. F. or even higher.
To prevent this intense heat from damaging the combustor before it exits to a turbine, a heat shield or combustor liner is conventionally provided in the interior of the combustor and on the dome plate of the combustor. The liner on the dome plate is often referred to as a splash plate and is particularly designed to shield the dome plate from radiation and the heat which it would induce in the plate. These non-structural segmented splash plates are impingement cooled by air passing through combustor dome impingement holes. Another source of potentially damaging heat is from the recirculating zones produced by the combustor air inlets including the swirlers. The recirculation scrubs hot air against the dome plate thereby further heating the dome plate by convection. This heat, particularly, that due to radiation, can warp and buckle the plate thereby damaging it as well as the air swirlers required to maintain optimum combustion conditions in the combustion zone.
Among the drawbacks of using protective liners or splash plates is that splash plates add weight, fabrication, complexity, and require significant impingement cooling air flow. These consequences are particularly undesirable in the design and manufacture of aircraft engines. Splash plate cooling is a source of unwanted hydrocarbon and carbon monoxide emmisions at low power engine settings. The impingement cooling air, after being used for cooling the splash plate, must exit the dome region and by so doing tends to quench the low power or idle flame in the combustor, thereby producing elevated levels of hydrocarbons and carbon monoxide. The present invention provides a multi-hole film cooling means to cool the dome plate without the need for a splash plate and the use of impingement cooling air.
Film cooling combustion liners downstream of the dome using circumferentially disposed rows of film cooling slots is well known as illustrated in U.S. Pat. No. 4,566,280 by Burr and U.S. Pat. No. 4,733,538 by Vdoviak et al. which are typified by a hollow annular ring, often referred to as a nugget, with cooling air feed holes operable to direct cooling air into the hollow chamber in the ring and slotted outlets. The outlets are operable to inject the cooling air onto the surface of the liner so as to entrain the cooling air in the boundary layer to form a cooling film over the hot surface of the liner.
Multi-hole film cooling has been developed for use in combustor liners and a more detailed discussion of the related art may be found in r U.S. Pat. No. 5,181,379 entitled "GAS TURBINE ENGINE MULTI-HOLE FILM COOLED COMBUSTOR LINER AND METHOD OF MANUFACTURE", invented by Wakeman et al., filed Nov. 15, 1990, assigned to the same assignee and U.S. patent application Ser. No. 07/631,855 entitled "MULTI-HOLE FILM COOLED COMBUSTOR LINER WITH SLOTTED FILM STARTER", by, Phillip D. Napoli, filed Dec. 21, 1990, assigned to the same assignee, and both are incorporated herein by reference.
Combustor domes do not have significant boundary layer flow along their hot surfaces as do combustor liners. Combustor dome plate flow is further distinguished from liner flow in that the combustor flow is generally a hot recirculatory jet flow generally perpendicular to and towards the dome plate unlike the flow along the combustor liner which is essentially parallel to the hot surfaces of the liner.
Combustor designers realize that effective film cooling, one which provides maximum film coverage, requires a great deal of cooling air and the multi-hole film cooled liner helps to minimize the amount of air used to accomplish this. The present invention provides a means for providing an effective combustor dome plate cooling film, increasing the film's effectiveness while realizing the efficiency benefits of the multi-hole designs.